Neutering: the honest picture
Once routine and automatic, now a conversation about timing rather than a yes or no.
What it reliably does
Prevents unwanted litters. In females, removes the risk of pyometra — a serious uterine infection that is common in unspayed older bitches and often needs emergency surgery — and reduces mammary tumour risk, substantially so when done before or shortly after the first seasons. In males, removes testicular cancer risk and reduces prostate problems.
What it does not reliably do
It is not a behaviour fix. Neutering reduces hormonally driven behaviours such as roaming, marking and some male-male tension. It does not address fear-based aggression, reactivity or anxiety, and in some anxious dogs removing testosterone can make fearfulness slightly worse. Behaviour problems need training and often professional help, not surgery.
Timing is the real question now
The old default was six months for everything. Current thinking is more nuanced, because sex hormones contribute to closing growth plates. Neutering large and giant breeds very early has been associated in several studies with higher rates of certain joint problems and some cancers, so many vets now advise waiting until closer to skeletal maturity in those breeds.
Small breeds mature earlier and this concern applies less. Cats are usually neutered around four to six months, before they can breed and before spraying becomes established. Because the picture varies by breed, size and sex, this is genuinely a conversation to have with your own vet rather than a rule to look up.
The weight gain nobody mentions
Neutering lowers resting metabolic rate appreciably. Portions that were correct before surgery become too generous afterwards, and post-neuter weight gain is extremely common. Reduce the daily amount within a few weeks of surgery rather than waiting to notice.
Recovery
Usually ten to fourteen days of restricted activity: lead-only toileting, no running, jumping or stairs, and no bathing. A recovery suit or collar prevents licking, which is what causes most wound complications. Contact your vet about swelling, discharge, a wound that opens, lethargy beyond the first day, or refusal to eat.
Alternatives
Chemical castration implants provide a reversible, temporary effect in male dogs and can be used to preview the behavioural change before committing. Ovary-sparing spay and vasectomy are available in some places for owners who want sterility without removing hormones. Both are worth asking about if timing is your main concern.
Timing by size and sex, in more detail
The research that changed practice looked at joint disorders and certain cancers in dogs neutered before skeletal maturity. The effect is size-dependent, which is why a single age no longer applies to every dog.
| Group | Common current guidance | Reasoning |
|---|---|---|
| Small dogs (under 10kg) | From around 6 months | Growth plates close early; joint risk is not the concern it is in larger dogs |
| Medium dogs | Around 9–12 months | Balance of skeletal maturity against unwanted litters |
| Large dogs | 12–18 months | Growth plates close later; several studies link early neutering to higher joint disorder rates |
| Giant dogs | 18–24 months | Latest maturity of all |
| Female dogs | Often after the first season, or 3 months after | Mammary tumour protection is greatest when done early, so this is a genuine trade-off to discuss |
| Cats | 4–6 months | Sexual maturity arrives early; spraying and roaming become habits once established |
The female dog row contains the real tension. Spaying before the first season gives the strongest protection against mammary tumours, but earlier surgery in large breeds carries the joint concerns above. There is no answer that optimises both, which is exactly why it is a conversation with a vet who knows your dog rather than a rule.
Pyometra: the reason many vets still push for spaying
A uterine infection that affects a substantial proportion of unspayed bitches by middle age. It typically appears a few weeks after a season, and signs include drinking more, lethargy, vomiting, a swollen abdomen, and sometimes a discharge — though in the closed form there is no discharge at all, which makes it harder to spot and more dangerous.
It is a surgical emergency, the operation is considerably riskier and more expensive than a routine spay because the patient is already ill, and it is fatal if untreated. Spaying removes the risk entirely.
What the surgery involves
Males. A short procedure through a small incision in front of the scrotum. Most dogs are noticeably themselves the next day, which is the main challenge — keeping them quiet.
Females. Abdominal surgery, either removing ovaries and uterus or ovaries alone, increasingly done laparoscopically where available. Recovery is longer and activity restriction matters more.
Both are done under general anaesthetic, typically as a day procedure with blood tests offered beforehand — worth taking up in older animals and in breeds with known anaesthetic sensitivity.
Recovery, day by day
- Day of surgery — grogginess, possible nausea. Offer a small light meal in the evening
- Days 1–3 — lead-only toileting, no stairs, no jumping. Pain relief given as prescribed even if they seem fine
- Days 3–7 — the risky window, because they feel better and want to run. Most complications start here
- Days 7–10 — post-op check, possible suture removal
- Days 10–14 — gradual return to normal activity
A recovery suit is generally better tolerated than a plastic cone and prevents licking just as well. Licking is what causes most wound breakdowns, and a wound that opens after a week is a far bigger problem than the original surgery.
Call the vet if you see
Swelling that grows, discharge or a bad smell, a wound edge that separates, lethargy beyond the first day, refusal to eat after 24 hours, vomiting, or straining to urinate.
Behaviour: what changes and what does not
| Behaviour | Likely effect |
|---|---|
| Roaming to find mates | Substantially reduced |
| Urine marking | Often reduced, especially if done before it becomes habit |
| Male-male tension over females | Often reduced |
| Mounting | Variable — often partly learned rather than hormonal |
| Fear-based reactivity | No improvement; occasionally slightly worse in anxious dogs |
| Guarding, chasing, pulling, barking | No effect. These are training matters |
Get an accurate daily portion
Enter weight, life stage and your food's calorie content for grams per day and per meal.
Open the food calculator →Energy needs drop after neutering, often by around a fifth, and weight gain in the months afterwards is the most common avoidable side effect. Check body condition →
Common questions
When should I neuter my dog?
It depends on breed and size. Small breeds are often done around six months, while many vets now advise waiting until closer to skeletal maturity for large and giant breeds because of joint development. Discuss timing with your own vet.
Will neutering calm my dog down?
Not reliably. It reduces hormonally driven behaviours such as roaming and marking, but does not address fear-based aggression, reactivity or anxiety, which need training rather than surgery.
Do pets get fat after neutering?
They can. Neutering lowers resting metabolic rate, so the same portion becomes too generous. Reducing the daily amount within a few weeks of surgery prevents most post-neuter weight gain.
Should I let my dog have a season before spaying?
It is a genuine trade-off. Spaying before the first season gives the strongest protection against mammary tumours, but in large and giant breeds earlier surgery has been linked to higher rates of joint problems. Discuss it with a vet who knows your dog's breed and size.
What is pyometra?
A uterine infection affecting a significant proportion of unspayed bitches by middle age, usually appearing a few weeks after a season. It is a surgical emergency and fatal if untreated. Spaying removes the risk entirely.
How long is recovery after neutering?
Usually ten to fourteen days of restricted activity. Days three to seven are the riskiest, because the animal feels well and wants to run. A recovery suit prevents licking better tolerated than a cone.